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Josias Aurel
Josias Aurel

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The difference between String and string in Typescript

TypeScript is a good advancement in the javascript ecosystem.
Today we are going to talk about the difference between the String and string types in Typescript.

Type error: Type 'String' is not assignable to type 'string'.
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Let's take a look at the above error.

To begin, we know that whether we use String or string, we would want to refer to the same thing. But both of those are a little different.

String is a class in JavaScript to construct strings. It provides a way of creating strings using that constructor. What we get using String is an object.
If you check if it's a string or not, you will get *

let name = new String('Mike');
console.log(typeof name); // object
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string on the other hand does not exist in JavaScript. Rather it is used in Typescript to tell it it is an actual string.

Therefore, when you are creating a function, type or interface in Typescript, it is recommended to use lowercase string to tell Typescript you want to get an actual string. If you use String, then you will get an object (which is not what you would want).

Thank you for reading.

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Top comments (0)

This post blew up on DEV in 2020:

js visualized

🚀⚙️ JavaScript Visualized: the JavaScript Engine

As JavaScript devs, we usually don't have to deal with compilers ourselves. However, it's definitely good to know the basics of the JavaScript engine and see how it handles our human-friendly JS code, and turns it into something machines understand! 🥳

Happy coding!